A dental handpiece generally has a grip section mainly composed of, as shown in FIGS. 6 and 7, generally cylindrical motor casing 90, motor unit 91 detachably accommodated in the motor casing 90 and supplying driving force to a dental tool, generally cylindrical end cap 92 connected to hose 93 which accommodates power cords for supplying power to the motor unit 91, and detachably connectable to the proximal end of the motor casing 90 and, and motor-unit-side connector 94 and power-cord-side connector 95 arranged between the motor casing 90 and the end cap 92 for electrically connecting the motor unit 91 and the power cords in the hose 93. The motor-unit-side connector 94 includes a plurality of pins 941, which are connected to the motor unit 91 and arranged in parallel in the opening of the motor casing 90 at its end to be connected to the end cap 92 as shown in FIG. 8. The power-cord-side connector 95 includes a plurality of sockets 950 for connectively receiving the pins 941 on the motor unit side. The sockets 950 are arranged slightly projecting outwards from the opening of the end cap 92 at its end to be connected to the motor casing 90. By connecting the motor casing 90 to the end cap 92 as shown in FIG. 9, the motor unit 91 and the power cords in the hose 93 are electrically connected. The end cap 92 has a distal end having a larger diameter which is the same as the diameter of the proximal end of the motor casing 90, and a proximal end having a smaller diameter and capable of receiving the hose 93 therein, and has a contour tapered from the distal to proximal end. The smaller diameter part in the proximal end portion functions as a sensor detectable part, at which an instrument hanger of a dental unit detects whether the motor is in use or not.
In this way, the grip section of a dental handpiece is composed of five parts, namely the motor casing 90, motor unit 91, connectors 94, 95, and end cap 92 (sensor detectable part). The motor-unit-side connector 94, specifically the pins 941, is arranged in the connecting-end opening of the motor casing 90, while the power-cord-side connector 95, specifically the sockets 950, is arranged slightly projecting outwards from the connecting-end opening of the end cap 92, so that the connectors 94 and 95 are connected in the connecting-end opening of the motor casing 90. Due to this structure, the connecting area between the motor unit 91 and the power cords in the hose 93 becomes long, which increases the length and weight of the overall grip section. Such a long, heavy handpiece imposes a work burden on dentists and dental technicians, who use a handpiece all day long.
In order to overcome this drawback, there is proposed a light and compact dental handpiece for reducing the work burden on dentists and dental technicians even their work lasts for a prolonged period of time. Patent Publication 1 discloses an example of such a dental handpiece, wherein motor M is connected to hose C (flexible tube) without a separate coupling. In this handpiece, by direct connection, the connecting area between the motor M and the hose C is minimized, which remarkably reduces the overall length and weight of the handpiece, especially of the grip section.    Patent Publication 1: JP-2009-148569 (see paragraph 0005 and FIG. 1)
However, in dental treatment, tools are usually sterilized after each treatment in order to prevent in-hospital infection of various pathogens between patients, and the motor is detached from the hose and subjected to autoclaving and the like treatment. With the above-mentioned conventional dental handpiece wherein the motor and the hose are directly connected, detachment of the motor is complicated, which lowers work efficiency. This problem is also discussed in paragraph 0005 of patent Publication 1.